1. Field of the Invention
This invention relates to absorption filter technology and more particularly relates to an apparatus system and method for poly-acrylic and polyvinyl based emissions filters.
2. Description of the Related Art
Fluorescence spectroscopy may be a key component of future micro-total-analysis-systems (uTASs), which may integrate the capabilities of entire laboratories onto compact devices consisting of microchips and other micro-fabricated elements (Lab-on-a-chip). A major component in fluorescence analysis is the optical filter that separates the excitation light from the fluorescence emission. Ideally, the optical filter component should be monolithically integrated to the lab-on-a-chip device, as well as simple to fabricate at low cost.
One simple approach to building a miniaturized imaging system capable of micro scale resolution is to directly couple the sensor array with the sample of interest, referred to as Contact Imaging. Contact image sensors, compared with conventional imagers, do not require optical elements, such as lenses between the sample and the sensor array, providing better collection efficiency without optical loss. Because of the very short distance between objects and the sensor surface, contact imaging systems have much greater collection efficiency. For objects in close proximity with the sensor surface, the contact imager subtends nearly 2π of the total solid angle, so the collection efficiency can be as high as 50% for samples that emit light. It was estimated that the optical efficiency of a contact imaging system is improved by 35 dB in comparison with camera-based imaging system.
Therefore it is possible to use a low power LED as an illumination source for dark objects because the improvement in collection efficiency allows the detection of a weak signal. The distance between the object of interest and the sensor array is mainly determined by the thickness of the optical filter and therefore thin filters are desired.
The earliest types of filters used at the micro-scale were interference filters or dichroic filters. An interference filter consists of multiple thin layers of dielectric material having different refractive indices and there also may be metallic layers. Interference filters are wavelength-selective by virtue of the interference effects that take place between the incident and reflected waves at the thin-film boundaries. The advantages with interference filters is that they can be fabricated using standard, low-temperature processes, they are compatible with integrated circuitry, can be readily integrated into larger microscale systems and arbitrary spectral profiles can be obtained using different layer arrangements. There are some serious disadvantages to interference filters, a variation of a few nanometers in the thickness of the layers can cause large errors in the cutoff wavelength, up to ±50 nm. Another limitation is that the spectral response of these filters depends on the angle of incidence of the incoming light. This is a major drawback in contact imaging due to the close proximity of the object of interest with the sensor array (<100 μm). Finally, it is not yet feasible to fabricate multiple filters of this type for different colors on one surface.
The referenced shortcomings are not intended to be exhaustive, but rather are among many that tend to impair the effectiveness of previously known techniques in fluorescence spectroscopy; however, those mentioned here are sufficient to demonstrate that the methodologies appearing in the art have not been satisfactory and that a significant need exists for the techniques described and claimed in this disclosure.